1. Field of the Invention
The present invention relates to a mobile communication technology, and, more particularly, to a communication of a mobile terminal in an area in which a private wireless network and a public wireless network mixedly exists.
2. Description of the Related Art
There is a dual mode terminal as a type of mobile terminals which can cope with a public PHS network that provides a public PHS (Personal Handyphone System) service and with a private PHS network that provides a private PHS service, respectively.
The dual mode terminal stores the subscriber numbers of the public PHS network and the subscriber numbers of the private PHS network and switches a subscriber number to be recognized according to a PHS network to be used.
However, when the dual mode terminal is located outside of a public PHS network's service area, even if a subscriber number of the public PHS network is dialed, the terminal of a communication partner cannot be called. On the other hand, when the dual mode terminal is located inside of a private PHS network's service area, the communication partner can be called by dialing an extension number or a dial-in number even if the dual mode terminal is located outside of the public PHS network's service area. As described above, a user of the terminal has to select a dial number according to the communication area of a present location each time the user transmits an outgoing communication.
Japanese Patent Application Laid-Open (JP-A) No. 2000-358280 proposes a method of overcoming the inconvenience of the user. According to the method of JP-A No. 2000-358280, when a terminal moves to a location outside a public service area and it is recognized that the terminal is located inside a private service area, the terminal automatically carries out an operation for transmitting an outgoing communication in a private mode and accesses to an exchange corresponding to PHS and registers it to transfer a response to the outgoing communication.
Further, recently, a system making use of an IP network as a private network has become widespread. An IP-PBX (Internet Protocol-Private Branch eXchange), which acts as an exchange for controlling a communication carried out by an IP terminal, is installed to the IP network. A technology making use of the IP-PBX is disclosed in, for example, JP-A No. 2002-319961.
However, when it is intended to construct a private network in an office, a lot of wireless base stations of the private network must be installed in the office to permit a terminal to move while holding a communication. In this case, a vast cost is necessary to introduce the private network. Accordingly, when a firm and the like intend to construct a private network for operation, a problem arises in that a vast investment is required.